<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<script>
    var app = 10;
    var App = 100;
    // 两个是不一样的
    console.log(app)
    console.log(App)
    // 不能用有特殊意义的↓
    // var var


</script>
</body>
</html>